Here are the titles which topped the charts of the Xbox Live most played games for the week of 7/3/06, straight from Major Nelson himself;

(Xbox 360) Top Live Games
1) Call of Duty 2
2) Ghost Recon 3
3) Oblivion
4) BFMC
5) Prey Demo
6) Final Fantasy XI
7) EA SPORTS™ Fight Night Round 3
8) 2006 FIFA World Cup
9) PGR3
10) Perfect Dark Zero

(Original Xbox) Top Live Games
1) Halo 2
2) Battlefield 2: MC
3) Counter-Strike
4) Splinter Cell Chaos
5) Rainbow Six 3 BA
6) Star Wars: Battlefront 2
7) Pro Evolution Soccer 5
8) Madden NFL 2006
9) Forza Motorsport
10) Splinter Cell Chaos

Mr. Nelson apologized for not being able to give title-specific data, but he did say that if both lists were combined, Halo 2 would be number 1 on the chart (followed by all 360 games).